Recently, organic EL displays have attracted attention as the next-generation flat display panels. The organic EL displays have such advantages as self-luminescence, wide viewing angle, high-contrast image, thin profile, lightweight, and low power consumption.
Each of the organic EL devices that constitute an organic EL display generally includes an anode, a cathode, and organic layers disposed between the anode and cathode. The organic layers are composed of a light-emitting layer containing fluorescent molecules, and an electron conductive layer and a hole conductive layer which sandwich the light-emitting layer. Application of a voltage between the cathode and the anode causes the injection of electrons into the electron conductive layer from the cathode and the injection of holes into the hole conductive layer from the anode, with the result that the electrons and holes are recombined in the light-emitting layer to cause luminescence.
A manufacturing method of an organic EL display includes lamination of organic layers and thin-film electrodes, thicknesses of which are of the order of several tens of nanometers. This lamination process is conducted in a clean room. Nevertheless, it is not possible to completely rid the clean room of foreign material such as a particle derived from an organic layer manufacturing machine or other device or from the surrounding environment. For this reason, foreign material may be incorporated into the organic layer during manufacturing of an organic EL display.
When a voltage is applied between the anode and cathode in a state where the organic layer is contaminated with foreign material, it results in current leakage between the electrodes via the foreign material. Once current leakage occurred, more current is needed to make the organic layer luminescent, resulting in high power consumption and low luminescence efficiency.
Known techniques for preventing possible current leakage via foreign material incorporated into the organic layer include a laser repair method (see, e.g., Patent Literatures 1 to 10). The laser repair method is a process whereby current leakage via foreign material is prevented by laser irradiation of a portion (hereinafter also referred to as a “defect”) of organic layer contaminated with foreign material. Since the laser repair method involves high-energy laser irradiation, it may also thermally damage the surrounding region of the laser-irradiated region of organic layer; therefore, a larger area of organic layer may be destroyed than necessary. Moreover, the laser repair method suffers from a problem that it may destroy a protective layer for the organic layer, allowing oxygen and water to migrate into the organic layer to cause degradation of the light-emitting layer, which leads to generation of dark spots.
In an effort to overcome these drawbacks, several laser repair methods have been proposed whereby defects are selectively destroyed so that possible damage to portions of organic layer other than the defects can be avoided (see, e.g., Patent Literatures 11 and 12).
Patent Literature 11 discloses a laser irradiation method in which a weak laser beam is applied to the organic layer at the surrounding region of a defect rather than directly to the defect. When the surrounding region of a defect is irradiated with a laser beam, the energy of the laser beam propagates from the laser-irradiated region to the defect, forming a high-resistance region in the defect and preventing current leakage between the anode and cathode via the defect.
Patent Literature 12 discloses a method in which a laser beam is applied to a defect present in the organic layer or anode so that multi-photon absorption occurs exclusively at the defect. This makes it possible to destroy defects for avoiding current leakage between the anode and cathode via the defects, while reducing damage to regions other than the defect.